A wide variety of articles that incorporate the phenomenon of retroreflectivity have been developed for a wide array of uses. Retroreflective articles have the ability to return a substantial portion of incident light back towards the light source. This unique ability has promoted widespread use of retroreflective safety articles. Besides traffic and warning signs and the like, a wide variety of clothing and similar articles such as backpacks, and the like have incorporated retroreflective articles into them. Persons who work or exercise near motor vehicle traffic need to be conspicuously visible so that they do not get struck by passing motor vehicles. When retroreflective articles are worn, the retroreflectivity highlights a person's presence by retroreflecting light from motor vehicle headlamps.
Retroreflective articles typically have an optical lens element layer, a polymeric bead bond layer, a reflective layer, and may also have a substrate layer. The optical lens elements commonly are microspheres that are partially embedded in the polymeric bead bond layer. The reflective layer typically is aluminum, silver, or a dielectric mirror that usually is disposed on the embedded portions of the microspheres. Light striking the front surface of the retroreflective article passes through the microspheres and is reflected by the reflective layer to re-enter the microspheres where the light's direction is then altered to travel back towards the light source. Thus, for example, when a vehicle's headlamps strike a retroreflective article, some of the light from the headlamps is reflected back to the driver of the vehicle.
It is generally not necessary, or even desirable, that an entire worn article be retroreflective, so retroreflective appliqués are often used. These retroreflective appliqués can then be attached to an article of clothing or other article to prepare a retroreflective article. In some instances, retroreflective appliqués have been made by partially embedding a microsphere layer in a thermoplastic carrier web, applying a reflective material over the microspheres' protruding portions, and then forming a bead bond layer over the coated microspheres. Often a pressure sensitive adhesive is applied on the bead bond layer's back surface, and a release liner is placed over the adhesive until the appliqué is secured to a substrate. The completed appliqué (also sometimes referred to as a transfer sheet) is supplied to a garment assembler in this form, and the garment assembler secures the appliqué to an article of clothing by removing the release liner and adhering the appliqué to an outer surface of the article of clothing. The carrier is then separated from the appliqué to expose the microspheres so that the appliqué can retroreflect light.
A number of retroreflective articles have been prepared and described. Among the retroreflective articles that have been prepared are those with bead bond layers that include a polyurethane material. In Japanese Patent Publication No. JP 8-158268, a method of manufacturing a light reflective coating cloth is described in which a resin layer is formed on a fiber cloth in which the resin layer has as its main body a polyurethane resin containing a metal fine powder such as aluminum, and forming a single or mixed resin layer of polyacrylate resin or polyurethane resin containing spherical transparent glass beads on said resin layer with a dry coating method. U.S. Pat. No. 5,976,669 (Fleming) describes a retroreflective article with retroreflective elements embedded in a binder layer that contains a solid polyurethane. The polyurethane includes soft segments, hard segments, silicone moieties, and urethane moieties. PCT Publication WO 2009/011989 teaches a method for preparing vulcanizable retroreflective sheeting in which the method comprises providing a reaction mixture comprising at least one diisocyanate, at least one polyisocyanate, at least one polyol, at least one unsaturated polyol, and at least one chain extension agent, coating the reaction mixture on a carrier web that comprises retroreflective elements, curing the reaction mixture, and removing the carrier.